1. Field of the Invention
The present invention relates to a rotary power trowel machine for finishing concrete surfaces and more particularly to a quick adjustment mechanism for the pitch of the blades of a concrete power trowel.
2. Description of the Prior Art
Rotary power trowels have been used for many years to level and finish large concrete surfaces. Rotary power trowels include a driven rotatable trowel blade assembly having a plurality of radially extending, generally flat trowel blades which rest directly on the surface being finished. The trowel blades can be pivoted about their radial axis to change the pitch of the blades as required depending upon the characteristics of the concrete surface being finished.
U.S. Pat. No. 4,232,980 issued Nov. 11, 1980 to the assignee of the present invention discloses a rotary power trowel in which the pitch of the rotatably driven blades can be adjusted by rotating a knob or hand wheel at the upper end of an elongated control handle for the machine. Under certain circumstances, it becomes desirable to quickly change the pitch of the rotary trowel blades in order to obtain the desired finish on the concrete surface. Various efforts have been made to provide a quick adjustment of the pitch of the rotary trowel blades. The following U.S. patents illustrate various assemblies associated with the rotary trowel blades to quickly vary the pitch about their respective radial axes.
While the above patented devices disclose structures for rapid adjustment of the pitch of the rotary trowel blades, these prior structures do not provide a quick adjustment for the blade pitch which achieves the mechanical simplicity and ease of operability obtainable by the structure of the present invention.
The rotary power trowel of the present invention includes a unique quick adjustment for the blade pitch which enables the blade pitch to be rapidly and effectively adjusted. The unique blade pitch adjustment also quickly and easily locks the adjustment assembly in adjusted position and quickly and easily unlocks the assembly when it is desired to change the blade pitch. The quick adjustment assembly of this invention includes a control lever pivotally mounted on the shaft of the operating handle of the trowel at a position just forwardly of and between the handle bar grips on the operating handle. The control lever includes a trip handle extending upwardly from the control lever to be easily grasped by an operator holding the trowel by the handle bar grips.
The control lever is associated with a semicircular guide mounted longitudinally on the shaft of the operating handle of the trowel with the center of the semicircular guide coinciding with the pivot axis of the control lever. The trip handle is then operated to lock the control lever in any adjustment position selected around the semicircular guide. The opposite end of the control lever has an actuating rod or link pivotally connected thereto which extends forwardly into connecting engagement with one end of a pivot link also pivotally mounted on the shaft of the operating handle. The other end of the pivot link includes a partial circular segment. The cable connected at one end to the actuating mechanism for moving a swash plate associated with the rotary blades to vary their pitch angle in a well known and conventional manner has its other end wound around the partial circular segment of the pivot link.
By actuating the trip handle and pulling the control lever rearwardly (towards the handle bar grips), the connecting rod is forced forwardly (away from the handle bar grips) thus rotating the pivot link to cause the cable to move upwardly in the operating handle shaft. This upward movement of the cable depresses the actuating mechanism to move the swash plate downwardly and cause the trowel blade pitch angle to increase. When the control lever is pushed forwardly (away from the handle bar grips), the connecting rod moves rearwardly and the pivot link rotates to relax the tension on the cable. The weight of the trowel then causes the pitch angle to decrease to the extent permitted by the relaxed cable.
In one embodiment of the invention, the control lever and trip handle include a pivotal locking plate having a slot shaped opening which receives the semicircular guide. The pivotal locking plate locks the control lever to the arcuate upper and lower edges of the semicircular guide to prevent movement of the control lever. The trip handle includes a trigger mechanism that is actuated to move the locking plate out of locking engagement with the arcuate edges of the semicircular guide to enable the trip handle and lever to pivot in order to change the pitch of the blades. The trigger mechanism is preferably associated with the trip handle so that normal movement of the hand of the trowel operator into engagement with the trip handle will actuate the trigger mechanism to release the trip handle and lever from the guide when it is desired to reduce the pitch of the trowel blades by pivoting the locking plate to perpendicular relation to the guide. When the trip handle and control lever are moved in the direction to increase the blade pitch, the locking plate slot edges will move along the guide edges to permit movement of the control lever in the direction to increase the pitch and it is not necessary to operate the trigger mechanism when increasing the blade pitch with it only being necessary to pull the trip handle toward the handle bars of the control handle for the rotary power trowel.
In a second embodiment of the invention, the semicircular guide has notches on its underneath arcuate surface. The control handle and lever have a spring biased latch mechanism that engages these notches in a desired adjusted position. The latch mechanism is released by a depressable button-like projection in the upper end of the trip handle to release the lever from the guide and enable the control lever to be moved in either direction.
In both embodiments of the invention, the structural relationships of the operating components is important. The control lever handle is spaced a longer distance from the pivot point of the control lever on the operating handle shaft than the distance between the control lever pivot point and the point of connection with the connecting rod. Similarly, the distance between the point of connection of the connecting rod with the pivotal link is shorter than the radius of the circular segment of the pivot link. These differences in length to the respective pivot points of the control lever and pivot link provide a substantial mechanical advantage. This mechanical advantage enables the control lever to be pivoted in a manner to increase the pitch of the trowel blades even when all of the weight of the trowel is resting on the trowel blades. The weight of the trowel resting on the trowel blades maintains tension on the cable that connects to the swash plate actuating mechanism at all times. The mechanical advantage leverage built into the adjustment mechanism of the present invention allows the operator to increase the pitch of the blades with a minimum of effort. It also enables the operator to effectively control a decrease in the blade pitch by slowly moving the trip handle forwardly to whatever pitch angle is desired, even a zero pitch angle where the rotary blades lie flat on the concrete surface.
Accordingly, it is an object of the present invention to provide a quick adjustment mechanism for the pitch of radial blades in a rotary power trowel which can be quickly locked and unlocked to enable the pitch of the blades to be quickly adjusted.
Another object of the present invention is to provide a quick adjustment mechanism having a mechanical advantage linkage for efficient adjustment of the blade pitch and to reduce the force required to vary the pitch of the blades.
Still another object of the present invention is to provide a quick adjustment mechanism for the blade pitch of a power trowel incorporating a control lever having a trip handle oriented just forwardly of the handle bars on the operating handle of the trowel and extending above the operating handle for easy access by an operator of the trowel.
A further object of the present invention is to provide a quick adjustment mechanism in accordance with the preceding object in which the trip handle can be easily manipulated to lock and unlock the trip handle in relation to a semicircular guide rigidly affixed to and extending above the shaft of the power trowel operating handle.
A still further object of the present invention is to provide a quick adjustment mechanism for the blade pitch of a rotary power trowel in accordance with the preceding objects in which the control lever is pivoted at a central point on the operating handle of the trowel, a connecting rod is pivotally connected to the end of the control lever remote from the trip handle, the connecting rod is pivotally connected to a pivot link which is pivotally mounted on the operating handle, and a tension cable is connected to the pivot link on the side opposite the connecting rod. The tension cable extends downwardly along the operating handle to a point of connection with the swash plate actuating mechanism to vary the pitch of the blades with the mechanism of the control lever, connecting rod and pivot link providing a mechanical advantage leverage to enable the pitch of the blades to be adjusted with a minimum of force applied to the trip handle.
Yet another object of the present invention is to provide a quick adjustment mechanism as set forth in the previous objects in which the trip handle is lockingly engaged with the semicircular guide by a pivotal locking plate with a slot receiving the semicircular guide and locking the control lever and trip handle against movement by a wedging action against the arcuate upper and lower edges of the guide.
Yet a further object of the present invention is to provide a quick adjustment mechanism as set forth in the preceding objects in which the locking plate is released by a trigger mechanism incorporated into the trip handle to enable the locking plate to be unlocked with the locking plate enabling free movement of the control lever in a direction opposite to that in which the control lever becomes locked thereby enabling easy unlocking of the control lever and trip handle to enable the pitch of the blades to be reduced and enabling the pitch of the blades to be increased by moving the trip handle in an opposite direction without requiring the release of the locking plate by actuating the trigger mechanism thereby simplifying the adjustment of the blade pitch.
An additional object of the present invention is to provide a trip handle which has a latch mechanism engaging a plurality of indentations or notches on the semicircular guide with the latch being released by a trigger mechanism which releases the latch from the indentations in the semicircular guide, thus enabling the trip handle to move in either direction to decrease the pitch of the blades or increase the pitch of the blades.
A final object of the present invention to be set forth herein is to provide a quick adjustment mechanism for blade pitch of a concrete power trowel in accordance with the preceding objects and which will conform to conventional forms of manufacture, be of simple construction and easy to use so as to provide a device that will be economically feasible, long lasting and relatively trouble free in operation.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.